A concussion is a traumatic brain injury that temporarily affects normal brain function. Following a head injury, the eyes offer immediate and visible clues about a person’s neurological status because the visual system is a direct extension of the brain. The optic nerve connects the eyes to the brain, and several cranial nerves control eye movement and pupil response. Changes observed in the eyes can reflect underlying disruption or pressure within the brain. The techniques described here are for preliminary, layperson assessment only and are not a substitute for professional medical diagnosis or treatment.
Why Ocular Checks Are Crucial After Head Trauma
The eyes are intrinsically linked to the central nervous system, making them a sensitive barometer for brain health. Approximately half of the cranial nerves are dedicated to eye function, meaning even a mild traumatic brain injury can disrupt the complex pathways controlling vision and eye movement. Problems like swelling or increased pressure inside the skull can quickly compress or damage these delicate nerve structures.
The brainstem, which is responsible for autonomic functions like breathing and heart rate, also houses the centers that control the pupillary response. A change in how the pupils react to light can signal an issue in this lower part of the brain that governs basic survival functions. Assessing the eyes can reveal problems like difficulty with eye coordination or tracking movement. This ocular motor dysfunction is a common result of concussion that causes symptoms like blurred vision, dizziness, and eye strain.
Performing the Pupillary Light Reflex Test
The pupillary light reflex (PLR) test determines the integrity of the nerve pathways that control pupil size. To perform this check, find a dimly lit area where you can clearly observe the eyes. Ask the person to focus their gaze on a distant, stationary object to prevent the pupils from constricting due to the accommodation reflex.
Use a bright, focused flashlight and approach the eye from the side to avoid startling the person. Shine the light directly into one eye for about one to three seconds, observing the direct response: the constriction of the pupil in the illuminated eye. A normal response is a rapid, brisk constriction followed by a slight re-dilation.
Next, observe the consensual response by shining the light into the same eye but watching the reaction of the opposite, non-illuminated pupil. The non-illuminated pupil should constrict simultaneously and to the same degree as the illuminated one. Repeat the process on the second eye, checking both the direct and consensual responses. The pupils should be approximately equal in size before the light is introduced, a condition called isocoria.
A major red flag is a fixed or significantly dilated pupil, which indicates a failure of the nerve pathway to constrict. Another concerning sign is anisocoria, where one pupil is noticeably larger than the other, especially if the larger pupil does not react to the light. A sluggish reaction, where the pupil constricts slowly or incompletely, is also abnormal. These findings, particularly if new or worsening, can suggest significant brain injury or pressure.
Assessing Eye Movement and Alignment
Beyond the light reflex, the ability of the eyes to move together and track objects is an important indicator of neurological function. To check smooth pursuit, or eye tracking, hold a finger or small object about 18 inches in front of the person’s face. Ask them to follow the object with their eyes only, keeping their head still.
Slowly move the object in an “H” or cross pattern to test the full range of motion. Watch for jerky, staggered movements, known as saccades, or an inability to smoothly follow the target, which can suggest a deficit in motor control. The person should also be asked if they experience double vision, dizziness, or headache during this movement.
For convergence, the eyes’ ability to turn inward to focus on a near object, start by holding the target object at arm’s length. Slowly move the object toward the bridge of the person’s nose, asking them to keep it in focus. Note the point at which one eye drifts outward or the person reports seeing double. Normal convergence typically allows the eyes to focus until the object is very close, often within two inches of the nose.
Finally, observe the resting alignment of the eyes while the person is looking straight ahead. Look for obvious misalignment, where one eye appears to drift inward or outward (strabismus). Another sign to look for is nystagmus, which is the involuntary, rhythmic jerking or shaking of the eyes, indicating disrupted vestibular and ocular motor control.
When to Immediately Stop the Examination
While these checks are helpful for initial screening, certain signs indicate a medical emergency that requires immediate professional attention. If the person loses consciousness, even briefly, or becomes increasingly drowsy and cannot be easily awakened, the examination must stop immediately.
The appearance of one pupil being significantly larger than the other is a definitive warning sign that warrants an immediate trip to the emergency room. Other red flags include signs of a potentially severe injury:
- Repeated vomiting.
- A seizure or convulsion.
- A headache that worsens and does not go away.
- Difficulty with balance or slurred speech.
- Weakness or numbness in the limbs.
Any worsening of symptoms or significant change in personality or behavior requires prompt emergency transport.